Testing apparatus and method for microcircuit testing with conical bias pad and conductive test pin rings

ABSTRACT

The test system provides an array of test probes. The probes pass through a first or upper probe guide retainer which has a plurality of slot sized to receive the probes in a way that they cannot rotate. A plurality of flex circuits at the different heights engage bottom probe ends at their respective height levels and flex circuits continue the electrical connection from the probes to a load board. The test probes are bonded to the flex circuits by ring shaped flowable conductive material. The flex circuits are biased against a load board by an elastomeric pad of spaced part conical projections.

BACKGROUND OF THE INVENTION

Technical Field

The present invention is directed to equipment for testingmicrocircuits.

Description of the Related Art

As microcircuits continually evolve to be smaller and more complex, thetest equipment that tests the microcircuits also evolves. There is anongoing effort to improve microcircuit test equipment, with improvementsleading to an increase in reliability, an increase in throughput, and/ora decrease in expense.

Mounting a defective microcircuit on a circuit board is relativelycostly. Installation usually involves soldering the microcircuit ontothe circuit board. Once mounted on a circuit board, removing amicrocircuit is problematic because the very act of melting the solderfor a second time ruins the circuit board. Thus, if the microcircuit isdefective, the circuit board itself is probably ruined as well, meaningthat the entire value added to the circuit board at that point is lost.For all these reasons, a microcircuit is usually tested beforeinstallation on a circuit board.

Each microcircuit must be tested in a way that identifies all defectivedevices, but yet does not improperly identify good devices as defective.Either kind of error, if frequent, adds substantial overall cost to thecircuit board manufacturing process, and can add retest costs fordevices improperly identified as defective devices.

Microcircuit test equipment itself is quite complex. First of all, thetest equipment must make accurate and low resistance temporary andnon-destructive electrical contact with each of the closely spacedmicrocircuit probes. Because of the small size of microcircuit probesand the spacing between them, even small errors in making the probe willresult in incorrect connections. Connections to the microcircuit thatare misaligned or otherwise incorrect will cause the test equipment toidentify the die under test (DUT) as defective, even though the reasonfor the failure is the defective electrical connection between the testequipment and the DUT rather than defects in the DUT itself.

A further problem in microcircuit test equipment arises in automatedtesting. Testing equipment may test 100 devices a minute, or even more.The sheer number of tests cause wear on the tester pins makingelectrical connections to the microcircuit terminals during testing.This wear dislodges conductive debris from both the tester pins and theDUT terminals that contaminates the testing equipment and the DUTsthemselves.

The debris eventually results in poor electrical connections duringtesting and false indications that the DUT is defective. The debrisadhering to the microcircuits may result in faulty assembly unless thedebris is removed from the microcircuits. Removing debris adds cost andintroduces another source of defects in the microcircuits themselves.

Other considerations exist as well. Inexpensive tester pins that performwell are advantageous. Minimizing the time required to replace them isalso desirable, since test equipment is expensive. If the test equipmentis off line for extended periods of normal maintenance, the cost oftesting an individual microcircuit increases.

Test equipment in current use has an array of test probes that mimic thepattern of the microcircuit terminal array. The array of test probes issupported in a structure that precisely maintains the alignment of theprobes relative to each other. A retainer and probe guide align themicrocircuit itself with the test probes. The test probes, probe guide,and retainer are mounted on a probe card having conductive pads thatmake electrical connection to the test probes. The probe card pads areconnected to circuit paths that carry the signals and power between thetest equipment electronics and the test probes.

For the electrical tests, it is desired to form a temporary electricalconnection between each terminal on the die under test and acorresponding electrical pad on a probe card. In general, it isimpractical to solder and remove each electrical terminal on themicrocircuit being contacted by a corresponding electrical probe on thetestbed. Instead of soldering and removing each terminal, the tester mayemploy a series of electrically conductive pins arranged in a patternthat corresponds to both the terminals on the die under test and theelectrical pads on the probe card. When the die under test is forcedinto contact with the tester, the probes complete the circuits betweenrespective die under test probes and corresponding probe card pads.After testing, when the die under test is released, the terminalsseparate from the probes and the circuits are broken.

The present application is directed to improvements to a probe arraysystem capable of high performance testing for die with fine pitch.

There is a type of testing known as “Kelvin” testing, which measures theresistance between two terminals on the die under test. Basically,Kelvin testing involves forcing a current to flow between the twoterminals, measuring the voltage difference between the two terminals,and using Ohm's Law to derive the resistance between the terminals,given as the voltage divided by the current. Each terminal on the dieunder test is electrically connected to two contact pads on the probecard. One of the two pads supplies a known current amount of current.The other pad is a high-impedance connection that acts as a voltmeter,which does not draw any significant amount of current. In other words,each terminal on the die under test that is to undergo Kelvin testing issimultaneously electrically connected to two pads on the probe card—onepad supplying a known amount of current and the other pad measuring avoltage and drawing an insignificant amount of current while doing so.The terminals are Kelvin tested two at a time, so that a singleresistance measurement uses two terminals on the probe card and fourcontact pads.

In this application, the pins that form the temporary electricalconnections between the die under test and the probe card may be used inseveral manners. In a “standard” test, each pin connects a particularterminal on the die under test to a particular pad on the probe card,with the terminals and pads being in a one-to-one relationship. Forthese standard tests, each terminal corresponds to exactly one pad, andeach pad corresponds to exactly one terminal. In a “Kelvin” test, thereare two pins contacting each terminal on the die under test, asdescribed above. For these Kelvin tests, each terminal (on the die undertest) corresponds to two pads (on the probe card), and each pad (on theprobe card) corresponds to exactly one terminal (on the die under test).Although the testing scheme may vary, the mechanical structure and useof the probes is essentially the same, regardless of the testing scheme.

There are many aspects of the test beds that may be incorporated fromolder or existing test beds. For instance, much of the mechanicalinfrastructure and electrical circuitry may be used from existing testsystems, and may be compatible with the electrically conductive probesdisclosed herein. Such existing systems are listed and summarized below.

One particular type of microcircuit often tested before installation hasa package or housing having what is commonly referred to as a ball gridarray (BGA) terminal arrangement. A typical BGA package may have theform of a flat rectangular block, with typical sizes ranging from 5 mmto 40 mm on a side and 1 mm thick.

A typical microcircuit has a housing enclosing the actual circuitry.Signal and power (S&P) terminals are on one of the two larger, flatsurfaces, of the housing. Typically, terminals occupy most of the areabetween the surface edges and any spacer or spacers. Note that in somecases, a spacer may be an encapsulated chip or a ground pad.

Each of the terminals may include a small, approximately sphericalsolder ball that firmly adheres to a lead from the internal circuitrypenetrating surface, hence the term “ball grid array.” Each terminal andspacer projects a small distance away from the surface, with theterminals projecting farther from the surface than the spacers. Duringassembly, all terminals are simultaneously melted, and adhere tosuitably located conductors previously formed on the circuit board.

The terminals themselves may be quite close to each other. Some havecenterline spacings of as little as 0.1 mm, and even relatively widelyspaced terminals may still be around 1.5 mm apart. Spacing betweenadjacent terminals is often referred to as “pitch.”

In addition to the factors mentioned above, BGA microcircuit testinginvolves additional factors.

First, in making the temporary contact with the ball terminals, thetester should not damage the S&P terminal surfaces that contact thecircuit board, since such damage may affect the reliability of thesolder joint for that terminal.

Second, the testing process is more accurate if the length of theconductors carrying the signals is kept short. An ideal test probearrangement has short signal paths.

Third, solders commonly in use today for BGA terminals are mainly tinfor environmental purposes. Tin-based solder alloys are likely todevelop an oxide film on the outer surface that conducts poorly. Oldersolder alloys include substantial amounts of lead, which do not formoxide films. The test probes must be able to penetrate the oxide filmpresent.

BGA test contacts currently known and used in the art employ spring pinsmade up of multiple pieces including a spring, a body and top and bottomplungers.

United States Patent Application Publication No. US 2003/0192181 A1,titled “Method of making an electronic contact” and published on Oct.16, 2003, shows microelectronic contacts, such as flexible, tab-like,cantilever contacts, which are provided with asperities disposed in aregular pattern. Each asperity has a sharp feature at its tip remotefrom the surface of the contacts. As mating microelectronic elements areengaged with the contacts, a wiping action causes the sharp features ofthe asperities to scrape the mating element, so as to provide effectiveelectrical interconnection and, optionally, effective metallurgicalbonding between the contact and the mating element upon activation of abonding material.

BRIEF SUMMARY

The following summary is intended to assist the reader in understandingsome of the basic concepts of the present disclosure but not intended tolimit the scope of the invention.

Amongst other concepts the following is disclosed. A test system fortesting integrated circuits (IC) comprising any or all of the followingelements:

-   -   a. an upper probe guide plate having an array of spaced apart        upper apertures for receiving a test probe;    -   b. a lower probe guide plate having a like array of spaced apart        lower apertures, collinearly aligned with the apertures of said        upper guide, or receiving a test probe;    -   c. an elastomeric block have a like a like array of spaced apart        apertures, collinearly aligned with the passages of said upper        guide, for receiving a test probe;    -   d. a plurality of elongated test probes having a probe tip at        its distal end and a connecting end at its proximal end, and a        cross member extending generally orthogonally from each of said        probes, said cross member being of such extent that it cannot        pass through said upper apertures or said passages in said        elastomeric material;    -   e. said test probes passing through said upper and lower        apertures and said passages, with said cross member located        between said upper probe guide plate and said elastomer, so that        the bias force of the elastomer drives said probes upwardly        thorough said upper plate to a stop where said cross member        engages said upper plate;    -   f. said proximal ends of said test probes being group into a        plurality of subgroups, each of the ends in said subgroup having        the same height as measured from the lower probe guide relative        to other ends in that subgroup and wherein the proximal ends in        each of the subgroups having different heights relative to other        subgroups;    -   g. said subgroups being arranged with into a pattern with the        tallest probes being grouped together in a central region, and        successively shorter subgroups being groups around the periphery        of the adjacent taller probes; to thereby form a staggered        presentation of probes with the tallest in the central region        and descending therefrom;    -   h. a plurality of layers flex circuits having a plurality of        connection points for engaging the proximal ends of said test        probes, said flex circuits being laterally spaced apart in        planes corresponding to the heights of the subgroups, so that        one flex circuit corresponds to each subgroup,    -   i. a first of said flex circuits being configured to have its        connection points engaging said tallest probes in said central        region and successive flex circuits having their connection        points engaging the next successive subgroup of next tallest        probes with an aperture in said flex circuit corresponding to        the space occupied by prior taller probe subgroups, so that        successive flex circuits have progressively larger apertures        than the prior flex circuit.

Also disclosed is a method of connecting making electrical connectionsto ends of a matrix of electrical test probes in a testing system fortesting integrated circuits, comprising any or all the steps in anyorder of:

-   -   a. adapting the length of the probes in the matrix into        subgroups of differing heights, wherein the first subgroup        contains at least the tallest probes and wherein the second and        successive subgroups contains probes progressively shorter than        the adjacent subgroup and wherein the probes of the successive        subgroups contain probes which surround the adjacent taller        subgroup, so that the probes together for a staggered structure        with the tallest probes in a central region;    -   b. providing a plurality of stacked circuit boards corresponding        to the number of subgroups, each board having connectors        configured to reach a respective set of subgroup probes; wherein        the first of said boards being on the bottom of the stack and        the next successive boards being placed atop said board and        wherein each successive board includes an aperture in the        central region sufficient to allow taller probes to pass        therethrough without engaging that board; so that the tallest        probes will engage the bottom board and shorter probes will        engage successive boards.

Also disclosed is a method of testing integrated circuits (IC) with amatrix of probes having a top and bottom end, said probes correspondingin position to test pads on the IC, the method of any or all of thefollowing steps in any order, comprising:

-   -   a. forming an upper probe guide plate with a plurality of slots        to receive the top end said probes;    -   b. forming a bottom guide plate with a plurality of slots to        receive the bottom end of said probes;    -   c. forming a portion on said probes between said ends with an        increased cross sectional diameter; said diameter being larger        than said slot on said upper plate, and thereby forming an        upstop;    -   d. forming an elastomeric block around probes between said upper        and lower plates, and below said upstop;        so that, said elastomer will drive said increased diameter        toward said upper plate thereby providing a bias force on said        probes toward said IC.

Also disclosed is test system for testing integrated circuits (IC)comprising:

-   -   a. an upper probe guide plate having an array of spaced apart        upper apertures for receiving a test probe;    -   b. an anti-intrusion layer proximate said upper probe guide        plate, said layer having a like array of spaced apart lower        apertures, collinearly aligned with the apertures of said upper        guide, or receiving a test probe;    -   c. an elastomeric block have a like a like array of spaced apart        apertures, collinearly aligned with the passages of said upper        guide, for receiving a test probe;    -   d. a plurality of elongated test probes having a probe tip at        its distal end and a connecting end at its proximal end, and a        cross member extending generally orthogonally from each of said        probes, said cross member being of such extent that it cannot        pass through said upper apertures or said passages in said        elastomeric material;    -   e. said test probes passing through said upper and lower        apertures and said passages, with said cross member located        between said upper probe guide plate and said anti-intrusion        later, so that the bias force of the elastomer drives said        probes upwardly thorough said upper plate to a stop where said        cross member engages said upper plate;    -   f. said proximal ends of said test probes being group into a        plurality of subgroups, each of the ends in said subgroup having        the same height as measured from the lower probe guide relative        to cross member and wherein the proximal ends in each of the        subgroups having different heights relative to other subgroups;    -   g. a plurality of layers flex circuits having a plurality of        connection points for receiving engaging the proximal ends of        said test probes, said flex circuits being laterally spaced        apart in planes:    -   h. a first set of said circuits having arms each with an        aperture for receiving proximal ends of a test probe;    -   i. a solid conductive flowable element located on at least some        of said arms and having an aperture, the element aperture being        concentric with the aperture of said arm, so that a portion of        the proximal ends of said test probes can protrude through said        apertures.

Also disclosed is a system wherein said flowable element is a donutshaped ring sized to surround said arm aperture, said element includesflowable metal capable of flowing onto said proximal end of said testprobe thereby making an electrical connection between said test probeand arm.

Also disclosed is a system wherein said flowable element includes aflowable solder paste formed into a ring structure.

Also disclosed is a system wherein said flowable element includesmaterials which become liquid and flowable at a predeterminedtemperature above standard room temperature and solid at roomtemperature.

The system wherein at least some of said arms include a flow barrierportion applied spaced from said aperture, said flow barrier configuredto block the flow of flowable conductive material from flowing beyond afixed point on said arm.

Also disclosed is a system wherein said barrier includes anon-conductive material bonded to said arm to provide a physical barrierto flowable material.

Also disclosed is a system wherein said barrier has a distal endproximate said aperture which is concave.

Also disclosed is a system for testing integrated circuits (IC)comprising:

-   -   a. a plurality of elongated test probes having a probe tip at        its distal end and a connecting end at its proximal end,    -   b. a plurality of layers flex circuits having a plurality of        connection points for receiving the proximal ends of said test        probes, said flex circuits being laterally spaced apart;    -   c. a first set of said flex circuits having arms each with an        aperture for receiving proximal ends of a test probe at one end        and termination points at another end; said other end having a        first face for electrical contact with a load board and second        back opposite said first face;    -   d. a compression pad including a plurality of adjacent conical        elastomeric projections applied to said opposite face with said        projections engaging said opposite face to apply bias pressure        on said other end of said flex circuit to maintain resilient        electrical contact between the load board and said flex circuit.

Also disclosed is a system wherein said conical projections include aplurality of closely spaced tapered projections.

Also disclosed is a method of applying force between a flex circuit anda load board in an integrated circuit testing device, the flex circuithaving a contact face having electrical contact points, and an oppositeface, the contact face being located adjacent the load board having likeelectrical contact points, comprising the steps of:

-   -   a. forming a pad of closely spaced resilient conical        projections;    -   b. locating said pad adjacent said opposite face, with said        projections in engagement with said opposite face,    -   c. applying pressure on said pad to compress said projections        into said opposite face,    -   d. thereby maintaining said electrical contact points        resiliently biased toward each other.

Also disclosed is a method of connecting probe bottom ends to a flexcircuit having probe apertures, in the testing integrated circuits (IC)with a matrix of probes having a top and bottom end, said probescorresponding in position to test pads on the IC, the method comprising:

-   -   a. inserting the probe bottom ends into apertures in the flex        circuit;    -   b. inserting a ring of flowable conductive material against said        apertures and concentric therewith;    -   c. heating the flowable materials to cause it to flow between        the ends and the flex circuit.

A method of applying force between a flex circuit and a load board in anintegrated circuit testing device, the flex circuit having a contactface having electrical contact points, and an opposite face, the contactface being located adjacent the load board having like electricalcontact points, comprising the steps of:

-   -   a. forming a pad of closely spaced resilient conical        projections;    -   b. locating said pad adjacent said opposite face, with said        projections in engagement with said opposite face;    -   c. applying pressure on said pad to compress said projections        into said opposite face;    -   d. thereby maintaining said electrical contact points        resiliently biased toward each other.

Also disclosed is a method of connecting probe bottom ends to a flexcircuit having probe apertures, in the testing integrated circuits (IC)with a matrix of probes having a top and bottom end, said probescorresponding in position to test pads on the IC, the method comprisingany or all of the following steps in any order:

-   -   a. inserting the probe bottom ends into apertures in the flex        circuit;    -   b. inserting a ring of flowable conductive material against said        apertures and concentric therewith    -   c. heating the flowable materials to cause it to flow between        the ends and the flex circuit.

Also disclosed is a method applying the ring to the flex circuit beforeinsertion of the said bottom ends.

Also disclosed is a method including applying the ring to the flexcircuit before insertion of the said bottom ends.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a probe array, minus the topprobe guide.

FIG. 2 is a perspective view of the probe array with probes protrudingto their up stop position.

FIG. 3 is close up of FIG. 2.

FIG. 4 is an exploded perspective view of the probe array.

FIG. 5 is a side perspective view with portions broken away of the pinstructure, elastomer and flex circuits.

FIG. 6 is a side plan view of FIG. 5.

FIG. 7 is a close up side perspective view of the engagement between thebottoms of the probes and flex circuits.

FIG. 8 is a plan view of the matrix of flex circuits as they are seenfrom the top or bottom.

FIG. 9 is a perspective view of probes in their elastomer.

FIG. 10 is a perspective view of probes protruding from the probe guideretainer.

FIG. 11 is a view like FIG. 10 except rotated 90 degrees.

FIG. 12 is an exploded perspective view of a second embodiment.

FIG. 13 is a side perspective view with portion broken away of a pinarray of a second embodiment. FIG. 13A is a figure like FIG. 13 exceptshowing pins of different height. FIG. 13B is a side perspective viewwith portions broken away of FIG. 13A. FIG. 13C is side plan view ofFIG. 13B.

FIG. 14 is a top perspective view of an anti-intrusion plate.

FIG. 15 is a figure like FIG. 14 showing the anti-intrusion platetransparently.

FIG. 16 is a side plan sectional view of FIG. 15.

FIG. 17 is a close up view like FIG. 13.

FIGS. 18A, 18B and 18C are perspective, top and side views of theelastomeric layer.

FIGS. 19A, 19B, 19C are partial side, top and partial side view of a pinand contact ball.

FIGS. 20A-C are side perspective views of parts of pins, 20A being a pintip showing a full pin, 20B is a partial perspective view, and tip 20Cis a partial side perspective view of the bottom portion.

FIGS. 21A-21B are top plan views of pins in rectangular holes and roundholes respectively.

FIGS. 22A-22B are close up views of upper portion tow pin types, akelvin (pin 22A) and a coaxial shielded pin (22B), additional views planand perspective views of the coaxial pin 242 are shown in FIGS. 22C-22H.

FIG. 23 is a perspective view of pins of various types in engagementwith flex circuit connection points include a double side by side pin242B.

FIGS. 24A-24B are perspective views of pins with a channel for conductorinlays.

FIGS. 25A-D are partial views of a pyramid style pin tip in side, front,other side plan view, and a perspective view.

FIGS. 26A-D are partial views of a chisel style pin tip in side, front,other side plan view, and a perspective view.

FIGS. 27A-D are partial views of a slant style pin tip in side, front,other side plan view, and a perspective view.

FIGS. 28A-D are partial views of a double chisel with rounded troughstyle pin tip in side, front, other side plan view, and a perspectiveview.

FIGS. 29A-D are partial views of a dome style pin tip in side, front,other side plan view, and a perspective view.

FIGS. 30A-D are partial views of a slot style pin tip in side, front,other side plan view, and a perspective view.

FIG. 31 is a close up partial perspective view of the connection betweenpins and flex circuit connection points.

FIG. 32A is a close up partial perspective view of an in-circuit devicein a flex circuit.

FIG. 32B is a single flex circuit layer and FIG. 33 is a close upperspective if of a flex circuit with coaxial shield.

FIG. 33 is close up partial view of the subject matter in FIG. 32B.

FIG. 34 is an exploded perspective view of the top portion of an arrayof test housings and flex circuits.

FIG. 35 is an exploded perspective view of the bottom portion of anarray of test housings and flex circuits.

FIG. 36 is a top plan view of several layers of flex circuits.

FIG. 37 is a top perspective view of one type of housing array.

FIG. 38 is a view like FIG. 37 with portion exploded away.

FIG. 39 is a side plan view with portion of the housing and stacked flexcircuits with the top layer folded away from the stack to avoid changesin impedance causes by adjacent layers.

FIG. 40 is a side plan view with portion of the housing and stacked flexcircuits with the top layer folded under the bottom later to avoidchanges in impedance causes by adjacent layers FIG. 41A is a close upschematic view of a via between flex circuits.

FIG. 41 is a schematic view of a bump pad via between flex circuits.

FIG. 42 is an exploded perspective view of a series of flex circuits inparallel arrangement on a housing.

FIGS. 43A and 43B are top and bottom perspective views of a clamp plateapplied to the housing.

FIG. 44 is a side perspective view of a retainer system for strainrelieve and for allowing lateral movement.

FIG. 45 is an exploded perspective view like FIG. 12 showing analternate embodiment.

FIG. 46 is a perspective view of portions broken away of a conicalelastomer to bias a flex circuit ribbon into contact with a load board.

FIG. 47 is a side cross sectional view of a portion of a flex circuitwith contact bumps.

FIG. 48 is a top perspective view of a sheet of conical elastomer.

FIG. 49 is a photographic view of a flex circuit ribbon from a pin arrayto a load board (not shown).

FIG. 50 is top perspective view of a single conical elastomeric element.

FIG. 51 is a top plan view of FIG. 50.

FIG. 52 is a slide plan view of FIG. 50.

FIG. 53 is a close up perspective view of FIG. 31 according to furtherembodiment.

FIG. 54 is a bottom perspective view of the subject matter of FIG. 53with portions removed.

FIG. 55 is a side plan view with portions broken away showing a pin andalternate embodiment donut joint.

FIG. 56 is a bottom plan view of FIG. 55.

FIG. 57 is a close up plan view a flex circuit trace with a receivinghole for a pin and a solder dam.

DETAILED DESCRIPTION OF THE DISCLOSURE

Consider an electrical chip, i.e. an integrated circuit that ismanufactured to be incorporated into a larger system. When in use, thechip electrically connects the device to the larger system by a seriesof pins or terminals. For instance, the pins on the electrical chip mayplug into corresponding sockets in a computer, so that the computercircuitry may electrically connect with the chip circuitry in apredetermined manner. An example of such a chip may be a memory card orprocessor for a computer, each of which may be insertable into aparticular slot or socket that makes one or more electrical connectionswith the chip.

It is highly desirable to test these chips before they are shipped, orbefore they are installed into other systems. It is even more desirableto test the chips while they are still on the wafer from which they wereformed. Such chips are called dice or an individual die, which can betested in situ by a prober (robot) which moves from die to die with amatrix of test pins aligned to engage the die pads perfectly. Suchcomponent-level testing may help diagnose problems in the manufacturingprocess, and may help improve system-level yields for systems thatincorporate the chips. Therefore, sophisticated test systems have beendeveloped to ensure that the circuitry in the chip performs as designed.The chip is attached to the tester, as a “die under test” (DUT), istested, and is then detached from the tester. In general, it isdesirable to perform the probe movement to the die and testing, asrapidly as possible, so that the throughput of the tester may be as highas possible.

The test systems access the chip circuitry through the same pins orterminals that will later be used to connect the chip in its finalapplication. As a result, there are some general requirements for thetest system that perform the testing. In general, the tester shouldestablish electrical contact with the various pins or terminals so thatthe pins are not damaged, and so that a reliable electrical connectionis made with each pin.

Furthermore, at the wafer level, the probes are so closely packedtogether, it is a technical challenge to find a way to connect leads tothe probes and then on to the probe card or equivalent.

A general summary of the disclosure follows.

The terminals of a die under test, DUT, at the wafer level are merelypads on the IC die and are probed by a robotic device which moves aprobe array into contact with the die. The probe will be brief but undera predetermined amount of force and the probe array must be able toabsorb the force without damage. Then the die/DUT is tested and theprobes must carry signals in and out of the chip to a probe card, (aterm used to characterize the circuit downstream from the probe array,and which may or may not be a physical pc board), and the retract andmove to another chip, not necessarily adjacent due to heat dissipationissues. Because the probe array is tightly packed, getting leads intothe matrix to extract the signals to a probe card or equivalent isproblematic. The present disclosure provides a solution which groups theproximal (nearest the probe card/farthest from the DUT) probe ends in togroups according to height with the tallest ones in a central region andprogressively shorter probes grouped together and surrounding the tallerprobes to progressively form a staggered structure with tallest probestoward the center and progressive rings of shorter probes toward theperimeter. Circuit boards, such as flex circuits corresponding to thenumber of subgroups, are stacked on each other and have proximal endswith connectors which reach to the various proximal probe ends in groupsaccording to their probe subgroup. The tallest probe(s) receive aconnector from a first flex circuit which reaches to such tallestprobe(s). The next tallest probe subgroup is reached by the next flexcircuit in the stack which has a plurality of connectors which surroundthe central region but have a void/aperture to allow the taller probesto pass therethrough to the prior flex circuit connectors. Thus thestack of flex circuits have progressively larger voids/apertures toallow the prior subgroup of probes to pass therethrough. In this mannerall of the probes in the matrix will be connected to a flex circuitwithout crossovers.

The preceding paragraphs are merely a summary of the disclosure, andshould not be construed as limiting in any way. The test device isdescribed in much greater detail below.

It will be understood that the terms top and bottom may be interchangedas they depend on the user's orientation.

Turning to the figures, FIG. 1 illustrates the bottom of a test system10 without the probe card, DUT/IC or prober, all of which are known inthe art. The system includes a lower probe guide 12, and upper probeguide 14, a matrix/plurality of test probes 16 and an elastomeric block18. It is noted that block 18 can be any bias material, includingsprings or elastomer tubes and the term “block” is to be interpretedbroadly as such. The preferred form is a plurality of tubular resilientmembers around each probe. They may or may not be joined together bybridges (to keep them unified). Such a structure will also be referredto as an elastomer block.

The upper and lower probe guides are plates which have apertures orslots which allow the passage of probe 18. They may be slotted with aparticular profile to prevent rotation of the probes if desired. Thepreferred material is ceramic but in any case a nonconductor or aconductor over coated with an insulator.

FIGS. 2 and 3 are top views which show the probes 18 as they extendthrough the top guide plate. The distance they extend out of the guideplate is determined by an up-stop feature explained below. The probecard 20 provides a circuit board to apply signals to the DUT.Interconnection between the probes 18 and load board 20 is by virtue ofa plurality of flex circuits 22 and connection block 24.

FIG. 4 illustrates the various layers of the preferred embodiment. Inthis embodiment, the upper probe guide 14 is received within the lowerprobe guide 12 and is retained therein by a circumferential edge on thelower probe guide which retains the upper probe guide. The elastomer canbe a block or a plate with a block portion as shown. The flex circuits22 are shown in layers 22 a, b, c, and d corresponding to the layers oneatop the other.

FIG. 5 illustrates the up-stop feature on the probes and theinterconnection between the probes and flex circuits.

The probes 18 have a distal end/or probe tip 18 a which engages the DUTat its contact points/pads. The tip can be many shapes as shown in USPublication No. US-2013/0002285-A1 hereby incorporated by reference. Theproximal end 18 b of probe 18 is preferably pointed so that it can bereceived and electrically engaged, perhaps soldered to contact points 30on the flex circuits 22.

Intermediate the ends 18 a/18 b is a cross member 19 which can be anorthogonal extension tangential to the longitudinal direction of theprobe or generally an increase in the diameter of the probe. Thefunction is to provide an up stop point for the probe so that it extendsout of the upper plate a predetermined distance which is suitable forthe prober.

Sandwiched between the upper and lower guide plates is an elastomer,preferably a block of compressible resilient material. It may be otherelastomers including a plurality of springs or a combination ofelastomers of different layers with different modulus of elasticity orresistance to compression if the probe deflection force needs to benonlinear or follow some preferred response.

In order to get signals in and out of the DUT via the probes, it isnecessary to provide an interconnect between the probes and probe card.In the preferred embodiment, this is achieved by flexible circuit boards22 which include at their distal end, a plurality of traces andconnection terminations 30 with holes to receive the sharp/dagger endsof the probes 18.

In order to reach all probes, it is necessary to adapt the length ofprobes into subgroups according to height with the tallest probes(tallest with respect to the lower probe guide) are in the center of thematrix (central region). FIG. 8 is a top view of the flex circuits. Flexcircuit 22 d and connection pads 30 populate the innermost and tallestprobes. The next flex circuit reaches to the next highest subgroup ofprobes which surround the first group. To achieve this flex circuit 22 chas a void/aperture 32 sufficient to allow the passage of the tallestprobes through to flex circuit 22 d. Looking to FIG. 4, 4 layers of flexcircuits are shown 22 a, 22 b, 22 c, and 22 d, and apertures 32 areprogressively larger from 22 d to 22 a so that the longest probes in thecentral region can reach the lowest flex circuit 22 d and each ring orsurrounding probe subgroup will reach progressively shallower flexcircuit contacts until the last flex circuit 22 a will make contact onlywith the shortest probes at the outermost peripheral edge of the probematrix.

FIG. 6 shows a close up view of the probes points 30, which arepreferably donut-hole circular probes with a hollow center with theprobe ends 18 b passing partly therethrough or otherwise connected.

FIG. 9 illustrates a view with the upper guide plate removed, revealingthe cross members 19 in abutment with the elastomer 16. As mentioned thecross member can be many configurations so long as they prevent passageof the probes through the upper guide.

FIGS. 10 and 11 show the probe tips 18 a from two angles. The preferredconstruction is a hollow point twin peak design though this disclosurecontemplates other shapes.

In addition to the structures disclosed, methods of manufacture aredisclosed.

For example, a method of connecting making electrical connections toends of a matrix of electrical test probes in a testing system fortesting integrated circuits is disclosed having any or all of thefollowing steps in any order.

-   -   a. adapting, such as but forming or cutting, the length of the        probes in the matrix of test probes, into subgroups of differing        heights, wherein the first subgroup contains at least the        tallest probes, and where the tallest probes are to be located        in a central region, like a skyscraper and wherein the second        and successive subgroups contains probes progressively shorter        than the adjacent subgroup of taller probes and wherein the        probes of the successive subgroups contain probes which surround        the adjacent taller subgroup, so that the probes together form a        staggered structure with the tallest probes in a central region        and probes of every diminishing height there around;    -   b. providing a plurality of stacked circuit boards, such a flex        circuit boards or other traces or leads, the number preferably        at least corresponding to the number of subgroups, each board        having connectors configured to reach a respective set of        subgroup probes ends; wherein the first of said boards being on        the bottom of the stack and the next successive boards being        placed atop said board and wherein each successive board        includes an aperture or in the central region sufficient to        allow taller probes to pass therethrough without engaging that        board; so that the tallest probes will engage the bottom board        and shorter probes will engage successive boards.

Also disclosed is a method of testing integrated circuits (IC) with amatrix of probes having a top and bottom end, said probes correspondingin position to test pads on the IC, having any or all of the followingsteps in any order of:

-   -   a. forming, such as by milling or casting, an upper probe guide        plate with a plurality of slots to receive the top end said        probes, the slots may be shaped to prevent rotation of the        probes,    -   b. forming a bottom guide plate with a plurality of slots to        receive the bottom end of said probes;    -   c. forming a portion on said probes between said ends with an        increased cross sectional diameter, such as a bulge or flare or        cross member etc.; said diameter being larger than said slot on        said upper plate, and thereby forming an upstop;    -   d. forming an elastomeric block around probes between said upper        and lower plates, and below said upstop; the block can also be        springs or other bias element;    -   so that, said elastomer will drive said increased diameter        toward said upper plate thereby providing a bias force on said        probes toward said IC.

FIGS. 12-43 illustrate an alternate embodiment of a housing and pinarray 110. The housing includes a plurality of pin groupings 112 eacharranged to test a different die from a wafer. In this FIG. 4 dice canbe tested simultaneously. A plurality of parallel stacks of flexcircuits 120 carried signals to and from the pins array groupings 112 aswill be explained herein. Underneath the flex circuit stacks 120 is aconductive bump interposer board 124 which includes an array ofconductive vias 140 on a via plate 144 (not shown in this figure, but inFIGS. 36 and 41B) which carry signals from the flex circuits to the loadboard (not shown). The bump plate is a non-conductor with a plurality ofconductive vias as shown in FIGS. 36 and 41B aligned with like contactson the flex circuits and load board. A temporary shipping plate 150 isshown but a load board of known art would be substituted.

To maintain electrical contact between the flex circuits, bump plate andload board, clamping plates 148 with bolts and nuts are provided.

FIGS. 13-18 illustrate the construction of the pin array 112. Pluralityof sliding pins 118, with pin tops 117 and 117 a, of differing height,which are arranged in an array according to the pad or ballconfiguration of the die. In FIG. 13 it can be seen that thisarrangement may not be rectilinear as in the prior embodiment but mayhave pins in any pattern as may be required. Pin height can also bevariable/uneven as shown in some figures.

As in the previous embodiment (FIG. 5) pins 118 include cross members119 (show in close up in FIG. 20B) which extend lateral and at generallyright angles to the length of the pin. These provide either an up ordown stop for the pin. The upper pin/probe guide 116 include a pluralityholes to receive the pins. The holes can be round or rectangular ifadditional anti rotation guidance is needed. See FIGS. 21A-B. The guideplate can also be further aided by a separate alignment plate 130 (seeFIG. 14 for detail) which includes a plurality of slots 131 shaped toreceive the pins and prevent their rotation.

To prevent the cross members 119 from intruding into the elastomericlayer/elastomer 140, an anti-intrusion layer (AIL) 132 is interposedbetween the alignment plate 130 (if used) and the elastomeric layer 140.The AIL prevents the cross members from cutting into the elastomer andultimately destroying it. Shown in greater detail in FIG. 15, the AIL130 includes a plurality of holes 133 large enough to accommodate thepin shaft but not allow the cross member 119 to path therethough. Theholes are of course aligned with the alignment and probe plate holes.Because the elastomer is resilient, downward deflection of the pins ispossible by the bias pressure of the cross member on the AIL which inturn compresses the elastomer 140 but cannot penetrate it.

The elastomer is also especially designed with a plurality of taperedholes 135 (FIGS. 18A-B, FIG. 17, FIG. 13) which are likewise alignedwith AIL holes. The holes in the elastomer are tapered from bottom totop as shown, and preferably with a conical shape. This taper has theeffect providing strain relief on the pins and to provide a more linearforce as the pins are deflected. Other hole shapes are possible so longas more material is removed from one end of the hole to the other toprovide a place for elastomer deflection and prevent nonlinearcompressive forces which would occur if there was build up. It wouldalso be possible to hollow out a portion of the passage way in theelastomer holes for the same purpose.

This embodiment includes a plurality of pin upper/top tip and bottom tipgeometries as shown in FIGS. 19-29. Pins 118 include a top tip 118 a anda lower portion tip/end 118 b. In FIG. 19A, a representation of a dieball contact 121 is shown. The pin upper tip 118 a in FIG. 19A is forkedhaving two lands 228 separated by a recess or trough 229. The troughprovides great contact force on the lands by reducing the contactsurface area and provides a debris catch/passageway. In FIG. 19C, thelower tip is shown with a center protrusion 230 which is sized to engageapertures in flex circuits (see below).

FIGS. 20A-C illustrates and alternate 4 point crowned tip 228 a-228 bwith a central valley 229 and arcuate valleys 229 a, 229 b on eitherside of the central valley/trough 229. A similar pin 118 a with tip isshown in FIG. 22A, however this pin a kelvin type which has separateforce and sense conductors 228 a, 228 b which are insulated from eachother by a central insulating strip 240 which is non conducting and thusthe conductive portions bonded on either side thereof carry the forceand sense signals.

FIG. 22B is a coaxial type pin 118 b which has a central conductorsurrounded on both sides by insulators 241 which provide a coaxialimpedance match as may be needed for high frequency tests. Bonded toinsulators 241 may be conductors 242 which can be used for shielding andto complete the coaxial structure. Such structures are also shown inFIG. 23.

A further pin embodiment 118 d is shown in FIGS. 24A-B. It has alongitudinal recess to receive a conductor (not shown) which will fillthe recess. This conductor insert (typically copper) provides lowerresistance than the remaining pin material.

In this embodiment, there is one crowned tip 240 a and a roof-peak tip240 b adjacent thereto. This may also be used for Kelvin environments.

FIGS. 25-30 are provided to illustrate alternative geometries.

FIGS. 25A-D illustrate a rooftop shape with a centerline and two slopingsides.

FIGS. 26A-D illustrate an inversion of FIG. 25 with a trough in place ofa peak and then two spaced part peaks with walls sloping to the troughand vertical outerwalls.

FIGS. 27A-D illustrate a single slope from one side to the other with aside ridge.

FIGS. 28A-D illustrate arcuate outer walls converging into a peak andthen receding into an arcuate trough.

FIGS. 29A-D illustrate an arcuate dome.

FIGS. 30A-D illustrate a pair of triangular wedges with a flat trough inbetween. Other tip geometries are also possible.

FIG. 31 shows the interconnection of the pin bottom ends 160 are shownconnected to flex trace fingers 322 having apertures 330. In thepreferred embodiment the ends 160 are soldered 335 or conductively gluedto the apertures.

Unlike the prior embodiment where the pins were of predetermined lengthand position, this embodiment contemplates pin locations and lengthsthat can vary according to need. Thus the rectilinear array shown inFIG. 5 with the longest pins in the central region, may not occur.

To accommodate this, a finger pattern structure as shown in FIGS. 33, 34and 35 is provided which show exemplary seven layers of flex circuitsconfigured to each end of each pin and to provide, as needed, coaxialground plane regions to maintain required impedances. These fingers arearranged to reach appropriate pins regardless of pin location. FIG. 34shows that multiple flex circuit layers can be applied atop each otherand by “reaching” the fingers to the required locations, it is notnecessary for certain pin to be joined only to designated flex layers asshown in FIG. 5. This also permits the use of ground plane fingers (i.e.fingers connected to ground) to surround certain pin contact points andother fingers to maintain desired impedances, such as illustrated inFIG. 32B. In FIG. 32B pins 160 are coaxially surrounded by ground planefinger 330 b which make not contact but provide impedance.

Likewise, for certain signals it may be necessary to amplify orotherwise condition the signals into or out of the pins. As shown inFIG. 32A, in-line active devices 340 can be put in series with thetraces to condition the signal. Also shown in FIG. 32A is how groundshielding can be accomplished by specific placement of ground traces 163on either sides of a signal trace 165. By adjustment of the spacingbetween the ground and signal traces, a coaxial shield can be created,which is especially valuable for high frequency signals.

FIG. 37 illustrates four of the seven layers of flex circuits shown 120a in FIG. 35. Region 360, show a ground shield area which surrounds apin connection and thereby maintains the required/desired impedance.

FIG. 36 illustrates a side by side parallel assembly flex circuit stacks120. A plurality of parallel stacks of flex circuits 120 carried signalsto and from the pins array groupings 112 as will be explained herein.Underneath the flex circuit stacks 120 is an optional conductive bumpinterposer board 124 which includes an array of conductive vias 140 on avia plate 144 which carry signals from the flex circuits to the loadboard. The bump plate is a non-conductor with a plurality of conductivevias as shown in FIGS. 36 and 41 b aligned with like contacts on theflex circuits and load board. A temporary shipping plate 150 is shownbut a load board of known art would be substituted in its place.

The plurality of side by side flex stack 120 are compressed by bracket380 which maintains the stacks, pins and (optional) bump plate incontact with the load board. By this side by side relationship, it ispossible to remove a single pin array and flex circuit stack as areplaceable cartridge from the adjacent arrays 112 so that quick andsimple replacement can be effected. FIG. 42 illustrated one stackremoved by removal of the c-clips 382 from studs 384.

FIG. 39 illustrates an alternate embodiment when the flex stacks 120 areoriented in different directions to each other typically two stacks areorthogonally oriented relative to their adjacent stack. This permitsdispersion of the contacts points along a greater portion of the loadboard so that the real estate on the load board is not as concentrated.In this configuration, any of the stacks can be removed without removalof adjacent stacks for similarly easy replacement.

FIG. 39 is a side sectional view of an array stack 120 and pin array112. In this figure, the top flex layer 120 a is wrapped under all ofthe other layers so that it is closest to the load board 150. Thisbrings the top layer directly to the load board and avoids the need fora pass through via 140, such as shown in FIG. 41. Such a via connection,passing adjacent other flex circuits may create unacceptable impedances.This is especially true for high frequency test points. It will beappreciated that additional flex layers may be looped under the bottomlayer, but this will quickly create the problem which was to be avoidedif too many are looped.

Alternatively, in FIG. 40B, top layer 120 a is extended laterally beyondthe stack 120 to provide another way to make direct connection to theload board. The methodologies of FIGS. 39-40 can be used together solong as the lateral extension of 40 is used for the layer above the tuckunder layer(s).

FIGS. 43A-B are top and bottom perspective views of the compressionplate 148 (also shown in FIG. 12) which compress the flex circuit stacksagainst the load board.

FIG. 44 is a view of a retainer system for holding stacks 120 inalignment. Studs 410 a pass through round holes in the flex circuitstacks 120. Holes 410 b pass through oblong holes 412 which allow forthe flex stacks to be clamped but remove any strain which may accumulatebetween the holes by allowing for some degree of X-axis movement toallow for tolerances.

FIG. 45 illustrates an alternate embodiment with a conical elastomerarray 502 (see also FIG. 48) which replaces the bump interposer board124 from FIG. 12. The flex circuit 120 (FIG. 46) shows a trace 123 whichruns from array of test pins 118 laterally to a reach an appropriatelocation on the load board (not shown). The conical elastomer provides afocused bias force against the flex circuit and consequently the loadboard so that contact on the flex circuit make solid electrical contactthe load board. A retainer or clamping plate 504 applies pressure tokeep the sandwich of layers in close electrical and physical contact.

FIG. 47 illustrates a cross sectional view of flex circuit 120 with AKapton® layer 508, a copper layer 510, a thicker Kapton® or polyamidelayer 512 and a further copper layer 514. A bump pad 520 is preferablynickel with gold plate for maximum conductivity when engaging the loadboard. FIG. 49 illustrates how the flex circuit bends to shiftlongitudinally from the plane of the bottom of the pin array to the loadboard plane so that the load board may be in a different plane(non-coplanar) but preferably in parallel spaced apart planes).

FIGS. 50, 51, and 52 illustrate a preferred embodiment for a conicalelastomeric bias element or compression pad. The basic function is toprovide a bias force against the flex circuit (or other contact arrayfrom the test pins) to the contact surfaces on the load board. The flexcircuit many contain hundreds of electrical contact points at regular orrandom locations on its surface so it is important to provide as manybias points as possible which align generally with the contact points.By providing a high density (high resistance to compression) matrix ofspaced apart cones, with spacing between the centers of the cones beingpreferably equal to or less than the average or mean spacing of contactpoints on the flex circuit or load board, there is a high likelihoodthat at least one cone will be located in line with at least part of acontact point, therefore providing the desired bias force. A flatelastomeric sheet is possible but providing a plurality of individualelastomeric bias points provides greater force per unit area so thecones will provide greater force on the contact points. In FIGS. 50-52,an individual contact point is shown apart from the sheet as a whole. Ithas a base substrate layer 560, a conical section 562, and a tip 564,which is preferably planar. As shown in FIG. 52, the conical section 562may be formed as a base segment 568 and a steeper conical segment 566.The material used may be of uniform resilience or the conical sectionand indeed the two conical segments may be formed with differentresilience by casting the sheet in different layers with differentmaterials. For example, the base substrate layer 560 may have ahigher/lower resistance to deformation than the layers in the conicalsection. The conical angle 570 may also be varied to alter theresistance to deformation. A planar tip may also be substituted with apointed tip. The conical elastomers may be formed in a mold with orwithout layers of different stiffness, the stiffer layer being towardthe conical portion. The conical shape is tapered from top to baseproviding a simpler way to remove the very small cones from a mold.Further, by using independent projecting elements, such as cones, thebias force has an independent suspension effect from cone to conefocusing most of the force into the load board, whereas a planar sheetwould transmit forces laterally potentially affecting other contactpoints. The cones may be hollow, solid or partially hollow, depending onthe resistance to compression desired.

FIGS. 53-57 provide an alternative structure and method for connectingpins to flex circuits. Pin ends 160 protrude through aperture 330 in theflex circuits trace fingers 322. In prior embodiments, solder balls wereused to join the pin ends to the fingers. In this embodiment, preformedconductive donut shaped rings 602 (see FIGS. 55-56) are provided.

Conductive donut rings 602 have an aperture 604 sized to mate with theaperture in the flex circuit. It is possible and perhaps desirable, tomake the aperture 604 smaller than the flex circuit aperture so thatmore of the pin tip 160 will engage the ring. The conductive ring may bea solder paste or other conductive material. It may be flowable solderwhich liquefies in response to heat to make a solid electrical bondbetween the tip and flex circuit. The tip 160 may be enhanced as shownwith vertical and horizontal cross members 620, 622 to increase thecontact surface area with the flex circuit and the conductive material.The tip may also be conical so that its narrow end can be more easilythreaded into the flex circuit aperture.

If the conductive material is flowable, then it will flow along the flexcircuit 322. It is desirable to limit the flow of such conductivematerial because its presence can change the impedance of the flexcircuit which may interfere with high frequency response. To minimizethis effect, a barrier 650 is applied to the flex circuit 322 whichstops the flow of any solder or other conductive joint material at thebarrier wall 652. The preferred barrier is a non-conductivepolyamide/plastic coating which bonds to the conductive flex circuitmaterial so that solder cannot flow underneath it. The preferred wallshape is arcuate as shown so that the flow will be shunted back to theflex terminal and spread out along the curved wall, thereby minimizingsolder build up. A concave wall is shown, a convex or other shape isalso possible.

The description of the invention and its applications as set forthherein is illustrative and is not intended to limit the scope of theinvention. Variations and modifications of the embodiments disclosedherein are possible and practical alternatives to and equivalents of thevarious elements of the embodiments would be understood to those ofordinary skill in the art upon study of this patent document. These andother variations and modifications of the embodiments disclosed hereinmay be made without departing from the scope and spirit of theinvention.

We claim:
 1. A test system for testing integrated circuits (IC)comprising: a. an upper probe guide plate having an array of spacedapart upper apertures for receiving a test probe; b. an anti-intrusionlayer proximate said upper probe guide plate, said layer having a likearray of spaced apart lower apertures, collinearly aligned with theapertures of said upper guide, or receiving a test probe; c. anelastomeric block have a like a like array of spaced apart apertures,collinearly aligned with the passages of said upper guide, for receivinga test probe; d. a plurality of elongated test probes having a probe tipat its distal end and a connecting end at its proximal end, and a crossmember extending generally orthogonally from each of said probes, saidcross member being of such extent that it cannot pass through said upperapertures or said passages in said elastomeric material; e. said testprobes passing through said upper and lower apertures and said passages,with said cross member located between said upper probe guide plate andsaid anti-intrusion later, so that the bias force of the elastomerdrives said probes upwardly thorough said upper plate to a stop wheresaid cross member engages said upper plate; f. said proximal ends ofsaid test probes being group into a plurality of subgroups, each of theends in said subgroup having the same height as measured from the lowerprobe guide relative to cross member and wherein the proximal ends ineach of the subgroups having different heights relative to othersubgroups; g. a plurality of layers flex circuits having a plurality ofconnection points for receiving engaging the proximal ends of said testprobes, said flex circuits being laterally spaced apart in planes: h. afirst set of said circuits having arms each with an aperture forreceiving proximal ends of a test probe; i. a solid conductive flowableelement located on at least some of said arms and having an aperture,the element aperture being concentric with the aperture of said arm, sothat a portion of the proximal ends of said test probes can protrudethrough said apertures.
 2. The system of claim 1 wherein said flowableelement is a donut shaped ring sized to surround said arm aperture, saidelement include flowable metal capable of flowing onto said proximal endof said test probe thereby making an electrical connection between saidtest probe and arm.
 3. The system of claim 2 wherein said flowableelement includes a flowable solder paste formed into a ring structure.4. The system of claim 3 wherein said flowable element includesmaterials which become liquid and flowable at a predeterminedtemperature above standard room temperature and solid at roomtemperature.
 5. The system of claim 1 wherein at least some of said armsinclude a flow barrier portion applied spaced from said aperture, saidflow barrier configured to block the flow of flowable conductivematerial from flowing beyond a fixed point on said arm.
 6. The system ofclaim 5 wherein said barrier includes a non-conductive material bondedto said arm to provide a physical barrier to flowable material.
 7. Thesystem of claim 6 wherein said barrier has a distal end proximate saidaperture which is concave.
 8. A test system for testing integratedcircuits (IC) comprising: a. a plurality of elongated test probes havinga probe tip at its distal end and a connecting end at its proximal end,b. a plurality of layers flex circuits having a plurality of connectionpoints for receiving the proximal ends of said test probes, said flexcircuits being laterally spaced apart; c. a first set of said flexcircuits having arms each with an aperture for receiving proximal endsof a test probe at one end and termination points at another end; saidother end having a first face for electrical contact with a load boardand second back opposite said first face; d. a compression pad includinga plurality of adjacent conical elastomeric projections applied to saidopposite face with said projections engaging said opposite face to applybias pressure on said other end of said flex circuit to maintainresilient electrical contact between the load board and said flexcircuit.
 9. The test system of claim 8 wherein said conical projectionsinclude a matrix of protections extending from a planar base mat, andwherein each cone has a top.
 10. The system of claim 8 wherein saidconical projections include a plurality of closely spaced taperedprojections.
 11. The test system of claim 10 wherein said flex circuitsextend laterally so that said electrical engagement with said probes islaterally offset from electrical engagement with the load board.
 12. Atest system for testing integrated circuits (IC) comprising: a. an upperprobe guide plate having an array of spaced apart upper apertures forreceiving a test probe; b. a plurality of elongated test probes having aprobe tip at its distal end and a connecting end at its proximal end; c.said proximal ends of said test probes being group into a plurality ofsubgroups, each of the ends in said subgroup having different heightsrelative to other subgroups; d. a plurality of layers flex circuitsgenerally in a first plane, having a plurality of connection pointsadjacent one end thereof for receiving engaging the proximal ends ofsaid test probes, said flex circuits being laterally spaced apart inplanes, and at an another end thereof, being configured to electricallyengage a load board located in a second plane generally parallel butspaced from the first plane: e. a first set of said circuits having armseach with an aperture for receiving proximal ends of a test probe; andf. the proximal end of each probe having a tip which is received withinthe aperture of said arm, so that the tip portion of the proximal endsof said test probes can protrude through said apertures and makeelectrical contact therewith.
 13. The test system of claim 12 furtherincluding a compression pad for biasing a portion of said flex circuitsinto engagement with said load board.
 14. The test system of claim 12wherein said compression pad including a plurality of adjacent conicalelastomeric projections applied to a portion of said flex circuitadjacent said load board maintain resilient electrical contact betweenthe load board and said portion of the flex circuit.
 15. The test systemof claim 14 wherein said conical projections include a matrix ofprotections extending from a planar base mat, and wherein each cone hasa top.
 16. The test system of claim 15 wherein said flex circuit has aplurality of electrical contact points intended to engage like contactpoints on the load board, and wherein the spacing between the tops ofeach cone is last than the average space between said contact points.